Messages in this thread Patch in this message | | | Date | Tue, 09 Jun 2009 02:39:52 -0700 | From | Greg KH <> | Subject | [patch 64/87] ptrace: simplify ptrace_exit()->ignoring_children() path |
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2.6.29-stable review patch. If anyone has any objections, please let us know.
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From: Oleg Nesterov <oleg@redhat.com>
commit 6d69cb87f05eef3b02370b2f7bae608ad2301a00 upstream.
ignoring_children() takes parent->sighand->siglock and checks k_sigaction[SIGCHLD] atomically. But this buys nothing, we can't get the "really" wrong result even if we race with sigaction(SIGCHLD). If we read the "stale" sa_handler/sa_flags we can pretend it was changed right after the check.
Remove spin_lock(->siglock), and kill "int ign" which caches the result of ignoring_children() which becomes rather trivial.
Perhaps it makes sense to export this helper, do_notify_parent() can use it too.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Roland McGrath <roland@redhat.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/exit.c | 25 ++++++++----------------- 1 file changed, 8 insertions(+), 17 deletions(-)
--- a/kernel/exit.c +++ b/kernel/exit.c @@ -703,19 +703,15 @@ static void exit_mm(struct task_struct * } /* - * Return nonzero if @parent's children should reap themselves. - * - * Called with write_lock_irq(&tasklist_lock) held. + * Called with irqs disabled, returns true if childs should reap themselves. */ -static int ignoring_children(struct task_struct *parent) +static int ignoring_children(struct sighand_struct *sigh) { int ret; - struct sighand_struct *psig = parent->sighand; - unsigned long flags; - spin_lock_irqsave(&psig->siglock, flags); - ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN || - (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT)); - spin_unlock_irqrestore(&psig->siglock, flags); + spin_lock(&sigh->siglock); + ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) || + (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT); + spin_unlock(&sigh->siglock); return ret; } @@ -728,7 +724,6 @@ static int ignoring_children(struct task static void ptrace_exit(struct task_struct *parent, struct list_head *dead) { struct task_struct *p, *n; - int ign = -1; list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) { __ptrace_unlink(p); @@ -750,12 +745,8 @@ static void ptrace_exit(struct task_stru if (!task_detached(p) && thread_group_empty(p)) { if (!same_thread_group(p->real_parent, parent)) do_notify_parent(p, p->exit_signal); - else { - if (ign < 0) - ign = ignoring_children(parent); - if (ign) - p->exit_signal = -1; - } + else if (ignoring_children(parent->sighand)) + p->exit_signal = -1; } if (task_detached(p)) {
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